Psychopathologists have increasingly emphasized the need for more research on the cognitive aspects of panic disorder. Unfortunately, most cognitive research has relied solely on patient self-report as the sole measure of cognition. Investigators have yet to apply the experimental paradigms of cognitive psychology to study cognition and panic. The major aim of the two experiments proposed here is to apply these paradigms to elucidate pathological information processing in patients with panic disorder. These studies involve the application of Stroop color-naming and semantic priming procedures to the investigation of the cognitive representation of fear, arousal, and catastrophe. The subjects are DSM-III-R panic disorder patients, normal subjects scoring high on the Anxiety Sensitivity Index (ASI; a questionnaire measure of the "fear of fear"), and normal subjects scoring low on the ASI. Psychiatric control subjects are obsessive-compulsive patients. Issues addressed include: Are cognitive representations of fear, arousal, and catastrophe characterized by ease and automaticity of activation in panic patients? That is, does such information reside in a primed state in declarative memory? Is this the basis for fearful thoughts "coming to mind" so readily in panic patients, and for the "catastrophic appraisal" of arousal sensations exhibited by panic patients? Are these representations linked in memory so that activation of one class of representation primes the others? Does direct induction of physiological arousal enhance these processing biases in panic patients? Is ease of activation uniquely associated with representations relevant to threat, or is positively valent emotional information also more accessible to awareness in panic patients? Is the hypothesized cognitive psychopathology of panic specific to panic disorder, or is it found in other anxiety-disordered patients as well (e.g., obsessive-compulsives)? Is the hypothesized cognitive psychopathology of panic found in normal individuals who score high on the ASI, a validated questionnaire measure of the fear of anxiety? If so, then this would suggest that the hypothesized cognitive psychopathology of panic may be a cause of panic disorder, and not merely its epiphenomenal consequence. It would also suggest that the ASI may identify individuals who are cognitively at risk for developing panic disorder.